1. Field of the Invention
This invention relates to an improved conduit stopper, used in pressurized conduit. The stopper is comprised of a solid, rigid carrier with two bendable forks that contain a deformable, flat sealing element. The external cylindrical surface of each fork is covered with a resilient sleeve member. The sealing element and resilient member cooperate in effecting sealing engagement with each other and with the interior surfaces of the conduit and with the cylindrical surface of the periphery of an access port that was cut into the conduit during a previous pressure tapping procedure. This improved conduit stopper design can be used in both temporary and permanent stopper installations, which is not true of any prior art device.
2. Description of the Prior Art
Pressurized conduit or piping systems convey fluids, both liquid and gas, in municipalities, industrial plants, and commercial installations. When originally installed, these conduit systems included certain block valves that could be closed to isolate sections of the conduit for repairs, relocation, or installation of new components into the conduit.
When such shutdowns are required in municipal distribution systems, it is frequently determined that too large an area will be deprived of water or gas service. Schools, hospitals, food processors, and commercial and industrial facilities may have to be shut down.
The total length of conduit to be depressurized can be greatly shortened by using one or more conduit stoppers, often in conjunction with existing block valves. A conduit stopper is a device that can be inserted into a pressurized conduit without prior service interruption, and the volume of fluids to be wasted is greatly reduced. Upon completion of work on the depressurized conduit, the stoppers are retracted from the conduit and block valves are opened, restoring flow through the repaired section of conduit.
Conduit stoppers are very well known in prior art under a variety of names, such as line stop, conduit stopper, conduitline plugger, inserting valve, add-on valve, insertable stopper valve, etc. Regardless of variation in construction, all conduit stoppers share one primary feature: the stopper is installed into a chamber adjacent to and communicating with the pressurized conduit. In most cases the chamber is a cylindrical nozzle that is assembled perpendicular and pressure-tight to the outside of the conduit. Communication is established by a process called pressure tapping. This process is well known in prior art, and utilizes a temporary tapping valve to allow different machines and apparatus to be mounted onto the conduit without loss of fluid pressure of flow.
The conduit stopper can then be installed through the valve into the nozzle chamber, where it is held until the conduit must be plugged. To stop flow in said conduit, the stopper is then moved from the nozzle into the conduit.
Many conduit stoppers use a solid, cylindrical, deformable plug, which engages in sealing contact with the inner walls of the conduit and the nozzle and with the cylindrical cut surface of the access port in the conduit. If such a deformable plug is unsupported, as is disclosed by Long: U.S. Pat. No. 3,799,182, the upstream fluid pressure capability rating of the stopper will be low, because increased pressure will further deform the unsupported plug into a failure shape that will allow leakage past the stopper, as taught by Murphy, et al: U.S. Pat. No. 5,690,139. With some rigid internal support, as taught by Thomas: U.S. Pat. No. 4,369,813, the pressure rating of the stopper is increased.
Higher stopper pressure ratings are attainable by providing substantial upstream and downstream external supports to a central, generally flat, deformable sealing member, as taught by Witt: U.S. Pat. No. 2,272,734; Lee: U.S. Pat. No. 2,789,244; Van Epps, et al: U.S. Pat. No. 3,115,163; and Murphy, et al: U.S. Pat. No. 5,186,199. However, as above disclosed, flat, deformable members, when acting alone, cannot totally pressure seal the conduit. Leakage flow passes vertically into the communicating nozzle chamber, because the thickness of the central sealing member does not fully close the area of the access port cut by the pressure tap.
Witt: U.S. Pat. No. 2,272,734 taught bendable metal carrier forks to sealingly contact the upstream and downstream cylindrical surfaces that were cut into the upper conduit metal wall during the pressure tap. The solid geometry was incorrect, precluding tight metal-to-metal seals. Lee: U.S. Pat. No. 2,789,244 taught a thick, cylindrical extension of the flat, central seal, which extension was deformed in the intersection between the conduit and the nozzle, thereby pressure sealing said intersection and blocking all flow and upstream fluid pressure.
Van Epps, et al: U.S. Pat. No. 3,115,163 disclosed a circumferential shoulder in each fitting nozzle to seal against a resilient, segmented O ring-type seal contained on each movable, rigid, stopper carrier fork. This segmented seal of the Van Epps improvement proved to be very fragile in the field, which resulted in frequent bypass leakage around the central flat sealing element. The Murphy, et al: U.S. Pat. No. 5,186,199 improvement restricted the downward force applied onto the segmented carrier seal, thereby increasing seal life.
Use of the nozzle shoulder presents both operational and logistical problems. The vertical location of the shoulder in each nozzle is critical in order to obtain simultaneous sealing action by both the flat central sealing element and the segmented xe2x80x9cOxe2x80x9d ring members. Specific vertical location of the sealing shoulder in each nozzle must be determined by the exact bore and wall thickness of the specific conduit into which the stopper nozzle is to be inserted.
Within any given nominal conduit size, for instance 8-inch, there may be more than 10 combinations of wall thickness and conduit outer diameter. Outer diameter of existing conduits can be determined either from records or by inspection. However, in emergency situations wall thickness is often unknown. Nozzles with improper shoulder locations are frequently installed, resulting in excessive leakage past the stopper.
The present invention totally eliminates the sealing shoulder in the nozzles of all fittings, thereby allowing shutdown using a single nozzle size for the full range of dimensional variation found in any given nominal conduit size.
Most conduit stoppers are intended for temporary service, often in emergency situations. When work is completed on the depressurized conduit, the temporary stopper is retracted, and the apparatus and tapping valve are removed under pressure and without interruption of service. The stopper fitting on the conduit is then protected with a closure device. The process can later be repeated under full fluid pressure using the original fitting.
Other conduit stoppers, such as Thomas: U.S. Pat. No. 4,369,813 and Long: U.S. Pat. No. 3,799,182, are designed specifically for permanent installation into a pressurized conduit. Each permanent conduit stopper is provided with an internal jackscrew-type actuating means that allows the conduit stopper to be operated as a conventional block valve that is opened and closed by a worker by merely turning a handle or a valve wrench. This type of permanent stopper can be used in emergencies in the same manner as a temporary stopper and then abandoned. However, the fitting material cost is considerably higher because of the self-contained jackscrew actuators. The present invention allows a temporary conduit stopper to later be converted into a permanent embodiment under pressure and with interruption of flow. The designs of prior art temporary conduit stoppers preclude later conversion without shutdown into permanent configurations.